The US National Institutes of Health (NIH) has proposed a broader definition of 'human embryonic stem cell' (HES), which would allow Federal funding of research using cells at an early development stage.

The NIH previously only allowed projects using HES generated from the blastocyst, an embryonic stage reached five days after fertilisation, to receive Federal funding. This excluded research using stem cells derived from younger embryos – called blastomeres – with only eight cells.

Massachusetts-based company Advanced Cell Technology is among the companies hoping to benefit from the new guidelines. The company filed a request with the US Food and Drug Administration (FDA) last year to test a treatment for Macular Degeneration - a degenerative eye disease - that uses blastomeres.

'It would have been a disaster to exclude these valuable human embryonic stem cell lines from consideration for federal funding, especially since the leftover embryos used to generate them meet all the NIH requirements', Dr Robert Lanza, the company's Chief Scientific Officer, told Reuters by e-mail.

Dr Lana Skirboll, director of the Office of Science Policy of the NIH, reportedly said: 'We are making what I think is a relatively small technical change to the definition of human embryonic stem cells…This changes none of the ethical requirements in the guidelines'.

Human embryonic stem cells (HES) are pluripotent cells, meaning they harvest the ability to differentiate into any type of cell; cardiac, neuronal or even immunological. This makes them interesting to scientists as they believe they could be key to treating diseases like stroke and heart disease.

When President Barack Obama took office, he removed some restrictions on the use of these cells. But the NIH still imposes strict ethical requirements and a review process on researchers seeking funding, according to Reuters.